Rectifier element



Patented May 16, 1950 RECTIFIER ELEMENT Carl C. Heln and John W. Stevcnhagen, Forest Hills, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application November 13, 1945, Serial No. 628,366

5 Claims. (Cl. 175-3366) Our invention relates to methods of improving the performance of copper oxide rectifiers and, in particular, relates to methods of improving the performance of copper oxide rectifiers which have been heated in an inert gas for a substantial period prior to oxidation of the copper.

One object of our invention is to increase the power output which a copper oxide rectifier of a given size is capable of delivering to a load.

Another object of our invention is to decrease the electrical resistance and heatingin the rectifler when current is flowing in the normally conductive direction therethrough.

Other objects of our invention will become apparent upon reading the following description.

Until quite recently the standard process for making copper oxide rectifiers has followed closely that described in the original Grondahl Patent No. 1,640,335 but has included the step of annealing the oxidized discs at a temperature of the order of 500 C. after oxidation for a period of about minutes. We have discovered that if the copper units are heated, before oxidation, to around 925 C. for a substantial period in a pure gas which is chemically inert at that temperature, and are then oxidized and subsequently annealed preferably at 400 C. for a protracted period of the order of several hours, a rectifier results which can withstand a high reverse voltage per disc and which will still have a relatively low resistance to current flow in the normaly conductive, or forward, direction but a high resistance to current in the normally-conductive or reverse direction.

All copper oxide rectifiers conduct a small amount of current in the direction in which they are normally non-conductive, but rectifiers which are given the above-described preliminary heattreatment in an inert gas show a reduction of this so-called reverse-current" to a small fraction of the value characteristic of rectifiers not so treated before oxidation; and they are found to be capable of rectifying much higher voltages per disc and ofwsupplying loads of much higher power than are rectifiers of the latter type. However, their resistance in the forward direction is also found to increase to an undesirable degree if annealed in accordance with the prior art schedule.

We have found that by subjecting rectifiers treated in an inert gas to an annealing operation, preferably at a, temperature of the order of 400 C. after oxidation, for a period of the order of hours in duration, this period extending with advantage even up to times of the order of sixteen 55 rectiflers may be quenched in water.

hours, their resistance to current flow in the forward direction is reduced to a minor fractionof the value shown when no such annealing is employed. At the end of the annealing term, the We have further found that, while the application of a similar annealing operation to rectifiers which have not been subjected to the inert gas treatment before oxidation will result in a decrease of resistance to current flow in the forward direction, this reduction of forward resistance is nowhere near as great for the non-gas-treated rectifiers as for the gas-treated rectiflers. We have further found that, while current flow in the nonconductive direction through the rectifiers is increased in both of the above cases by the annealing operation, the increase is relatively small in the case of the gas-treated rectifiers, and several times as large in the case of the rectifiers oxidized without inert gas pretreatment.

The foregoing results are illustrated by the following tabulations of the results of tests of rectiflers pretreated in inert gas and then oxidized before annealing for the various periods indicated. 1

Forward Volts for Reverse at- Anneal Time in Hours (lurreiillci 8121 After 1056 Initial hrs. at 80 C.

It is seen that the extension of the annealing time from the conventional fifteen minutes to fifteen hours results in halving the resistance to current flow in the forward" direction. This is an important achievement.

It may also be noted that while operation at C. for 1056 hours causes the forward resistance to increase by some percent in the case of rectiflers annealed for the conventional fifteen minute period, it causes an increase of only 58 percent in rectiflers annealed for 15 hours.

To give a specific illustration of how our invention may be practiced:

(1) Copper plates are degreased and given a bright dip in acid. (Bright dip can be eliminated if elements have sumciently good surface characteristics.)

(2) The units are strung on a rack and given 3 a 3-hour treatment in -pure carbon dioxide at 925' C., after which they are cooled to room temperature in this atmosphere.

(3) The units are then restrung on "burnedout rods (oxidation rods that are heated to 1055' C. for a sumcient period to eliminate foreign material placed on the rod during the quenching in tap water) and placed in the oxidation furnace at 1055' C. for a period of 11% minutes. Filtered air is circulated through the furnace during this time.

(4) The units are then removed from the oxidation furnace and placed in the annealing furnace at 400' C. for 15 hours.

(5) Following the anneal period the elements are quenched in tap water at room temperature.

(6) The black oxide is removed in the conventional manner by dipping in a 2% solution of sulfuric acid in water at 80' C. followed by a quick etch in concentrated nitric acid.

(7) An aquadag coating may be applied to the oxide surface for contact purposes.

While we have mentioned an anneal at 400' C. as a specific instance of a temperature to be used. annealing at any temperature throughout the range between 1000' C. and room temperature is within the purview of our invention. We have likewise found that annealing for periods of considerably under sixteen hours still produces a substantial improvement and, accordingly. annealing for periods of both less than sixteen hours and greater than sixteen hours is within the scope of our present disclosure.

In accordance with the patent statutes, we have disclosed a particular process for carrying out our invention, but it will be obvious to those skilled in the art that its principles are of broader application and by no means limited to the specific values which we have used as illustrations.

We claim as our invention:

1. The method of producing copper oxide units which comprises heating the mother copper to a temperature above 500' C. for a substantial period in an inert gas, oxidizing the copper at a temperature above 900' C., and annealing the resulting elements subsequent to oxidation at an elevated temperature for an extended period.

2. The method of producing copper oxide units which comprises heating the mother copper to 4 a temperature above 900 C. for a substantial periodinaninertgaaoxidisingthecopperat a temperature above 900' C., and annealing the resulting elements subsequent to oxidation at a temperature of the order of 400' C. for an extended period.

3. The method of producing copper oxide units which comprises heating the mother copper to a temperature above 500' C. for a substantial period in an inert gas, oxidizing the copper at a temperature above 900 C., and annealing the resulting elements subsequent to oxidation at an elevated temperature for a period of the order of sixteen hours.

4. The method of producing copper oxide units which comprises heating the mother copper to a temperature around 925' C. for a period of the order of three hours in carbon dioxide, oxidining the copper at a temperature above 900' C., and annealing the resulting elements subsequent to oxidation at an elevated temperature for a period of the order of sixteen hours.

5. The method of producing copper oxide units which comprises heating the mother copper to a temperature around 925' C. for a period of the order of an hour in carbon dioxide, oxidizing the copper at a temperature above 900 C., and annealing the resulting elements subsequent to oxidation at a temperature of the order of 400' C. for a period of the order of sixteen hours.

' CARL C. HEIN.

JOHN W. BTEVENHAGBN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,197,115 Randolph et al. Apr. 16, 1940 2,201,709 Williams et al. May 21, 1940 2,342,734 Rein Feb. 29. 1944 2,389,363 Hein et a1. Nov. 20, 1945 2,399,773 Weintrob May 7, 1946 FOREIGN PATENTS Number Country Date 115,729 Australia Aug. 27, 1942 

